[rdiff-backup-users] moving backup dir to external server produce errors

[me]

Hi all,
I had a rdiff-backup (1.2.8) that was setup to backup files locally (on 
the same server).
I ran out of space on this server so I have copied via scp the backup 
directory to another server like this :
scp -r /home/backup/web address@hidden:/home/server/backup/
Then I have modified the rdiff-backup script to send to the new location :
#!/bin/sh
nice -n 19 rdiff-backup /var/www address@hidden::/home/server/backup/web 
&& nice -n 19 rdiff-backup --remove-older-than 30B --force 
address@hidden::/home/server/backup/web
But now I getting lot of errors from email files and temp session files 
in this directory like this :
UpdateError web13/web/files/tmp/sess_fdfa4a5f841d931ff590a273f9022286 
File changed from regular file before signature
I've tried to use the --force option but it still produce the same errors.
Thanks a lot if you could assist a bit.
Nicolas Canonne